The present invention generally relates to electrical switch assemblies of the type including at least three separate contact terminals arranged within a switch housing, wherein one of the contact terminals electrically engages a normally energized or hot electrical conductor and each of the remaining contact terminals engages separate, normally non-energized or cold electrical conductors. A pushbutton actuator is arranged to establish an electrical circuit between the hot contact terminal and either of the cold contact terminals. Such a switch is referred to as an on-on switch, in that one of the two electrical circuits is always engaged, or on, as a result of each operation of the actuator.
To be effective, the referred-to switch should include an actuator capable of alternatively achieving two stable positions corresponding to the alternative electrical circuits established between the hot contact terminal and either of the remaining cold contact terminals. A pushbutton ratchet switch actuator capable of achieving two such separate stable positions is disclosed in co-pending Ser. No. 873,030, and incorporated by reference hereinabove. The pushbutton actuator includes a plunger ratchet mechanism which can be easily actuated by successive axial actuations of the plunger. By initially positioning each of the cold contact terminals on opposite sides of a moveable contact mounted on the plunger and electrically engaged with the hot contact terminal, it becomes possible to alternatively engage the moveable contact with either of the cold contact terminals, thereby creating an electrical circuit with either of the cold terminals.
Plunger ratchet mechanisms generally move their plungers beyond at least one of the stable positions to allow the ratcheting mechanism to index. In such case, the contact moved by the plunger will also travel past and then return to one of the stable positions. As a result, one of the cold contact terminals which is arranged to intersect and engage the moveable contact, will be forced to deflect beyond its normally tensioned engaged position to an even more highly tensioned position resulting from the indexing movement of the plunger. However, this extra bending tends to create fatigue in the terminal which can result in its premature failure. Fatigue failure of terminals is one of the most frequent causes of failure of known prior on-on switches.
A further problem confronting prior art assemblies is that after the contact has been repeatedly deformed, the contact tends to remain in the deformed position, preventing engagement with the moveable contact. If a spring biasing force is applied to ensure proper alignment of the cold terminal, such contact will resist deformation, causing the plunger mechanism to jam and preventing the required ratcheting action from occuring.
As will become clear hereinafter, the present invention provides an on-on electrical switch which overcomes the many disadvantages inherent in known prior art, as discussed above, as well as additional disadvantages confronting the known prior art.